High Data Rate (HDR) is an emerging mobile wireless access technology that enables personal broadband Internet services to be accessed anywhere, anytime (see P. Bender, et al., “CDMA/HDR: A Bandwidth-Efficient High-Speed Wireless Data Service for Nomadic Users”, IEEE Communications Magazine, July 2000, and 3GPP2, “Draft Baseline Text for 1xEV-DO,” Aug. 21, 2000). Developed by Qualcomm, HDR is an air interface optimized for IP packet data services that can deliver a shared forward link transmission rate of up to 2.46 Mbit/s per sector using only (1X) 1.25 MHz of spectrum. Compatible with CDMA2000 radio access (TIA/EIA/IS-2001, “Interoperability Specification (IOS) for CDMA2000 Network Access Interfaces,” May 2000) and wireless IP network interfaces (TIA/EIA/TSB-115, “Wireless IP Architecture Based on IETF Protocols,” Jun. 6, 2000, and TIA/EIA/IS-835, “Wireless IP Network Standard,” 3rd Generation Partnership Project 2 (3GPP2), Version 1.0, Jul. 14, 2000), HDR networks can be built entirely on IP technologies, all the way from the mobile Access Terminal (AT) to the global Internet, thus taking full advantage of the scalability, redundancy and low-cost of IP networks.
HDR has been adopted by TIA (Telecommunications Industry Association) as a new standard in the CDMA2000 family, an EVolution of the current 1xRTT standard for high-speed data-only (DO) services, formally referred to as HRPD (High Rate Packet Data), also known as 1xEV-DO or IS-856.
IS-856 systems are typically implemented using the radio access network architecture shown in FIG. 1. Here the Access Terminal (AT) 10 may be a laptop computer, a Personal Digital Assistant (PDA), a dual-mode voice/data handset, or another device, with built-in IS-856 support.
The entire administrative service area of a wireless access provider may be divided into one or more subnetworks (or subnets) 12, 14. Each subnet 12 includes a set of Radio Nodes (RN's) 16, 18 and one or more Radio Network Controllers (RNC) 20, 22. The RN's are connected to RNC's over a backhaul network 24. In existing 2G and 3G wireless networks, each RN is connected to only one RNC using dedicated leased lines or ATM permanent virtual circuits (PVC's). Further, RNC's are connected to each other using dedicated leased lines or ATM PVC's. In a new generation of IP-based radio access networks, the backhaul can be implemented using a shared IP or metropolitan Ethernet network which supports many-to-many connectivity between RN's and RNC's.
Each RNC typically controls 25-100 RN's. Each RN typically supports 1-4 carriers each of 1.25 MHz of bandwidth. Further, each cell area (not shown) is typically divided into multiple sectors (typically 3 or 6) and the RN has one radio transceiver 27 for each sector.
Each RNC is connected over an IP network 26 to one or more Packet Data Serving Node's (PDSN's) 28 (see TIA references cited earlier). The RNC communicates with the PDSN over a standard interface termed the R-P (Radio-Packet) interface 30. The R-P interface is further broken into two interfaces: the A10 interface used to carry data and the A11 interface used to carry signaling. A PDSN can be viewed as an edge router that supports mobility; it maintains link layer connectivity to AT's through the Access Network. The PDSN also interfaces to AAA servers 32 for Authentication, Authorization, and Accounting (AAA).
Once an AT connects to the network, it establishes session with an RNC and receives a link layer address from the RNC. The session represents all the information the RNC needs to serve the AT. In IS-856 radio access networks as currently defined by 3GPP2 in 1xEV-DO IOS Phase 1 (IS-878), each RN is uniquely associated with an RNC and each subnet contains only one RNC. As a result, when an AT moves from the coverage area of one RNC to the coverage area of another, the AT performs a handoff, which includes a session transfer.
Every time a dormant AT crosses a subnet boundary, the AT initiates a dormant handoff by sending a UATI_Request. The AT recognizes the need for a dormant handoff by monitoring the 128-bit SectorID being broadcast by the sectors. All sectors that belong to the same subnet have SectorID's that fall within a certain range. The 128-bit Universal Access Terminal Identifier (UATI) assigned to an AT in a given subnet falls within the same range. When the AT moves into the coverage area of another subnet, the AT compares its UATI with the SectorID being broadcast by its serving sector. When these do not belong to the same range, the AT knows that it has crossed a subnet boundary and initiates the dormant handoff by sending a UATI_Request.
A first purpose of a dormant handoff is to inform the PDSN to send packets arriving for that AT to the new serving RNC. Dormant handoffs involve a relocation of the R-P (A10) session from the old serving RNC to the new serving RNC. Without such handoffs, the PDSN would send packets to an old serving RNC. Since the old serving RNC does not know the location of the AT outside its subnet, AT's packets may be lost.
A second purpose of a dormant handoff is to transfer session information between RNC's. In IS-856, each RNC maintains certain session information about the AT. Such session information is needed for communication over the air interface. Session information includes the Universal Access Terminal Identifier (UATI), security keys for access channel authentication and encryption, and other protocol constants. Every time the AT crosses an RNC boundary (in this case a subnet), a new UATI needs to be assigned to the AT and the remaining session information needs to be transferred from the old serving RNC to the new serving RNC. Such a transfer requires a network link between the RNC's. Without such session transfer, every handoff between RNC's would result in a new and lengthy session establishment, taking up precious air resources and causing delays. When the footprint of an RNC is small, dormant handoffs occur frequently, resulting in excessive use of airlink resources (for the new UATI assignment), extra processing for the RNC's to implement the session transfer, and extra processing for the RNC and PDSN to relocate the A10 connection.